The present invention relates to U-shaped cup seals.
A prior art U-cup piston seal reproduced from Doutt U.S. Pat. No. 3,576,153 is illustrated in FIG. 2 of the drawings in its as-formed shape. The U-cup piston seal comprises an annular member 10 of resilient material having an arcuate inner surface 11 extending inwardly of the annular member and defining a portion of an annular flange 12 which is of smaller diameter than a secondary flange 13 formed in spaced relation thereto and immediately radially, outwardly thereof.
The area between the flanges 12 and 13 defines an annular groove 14 which extends well into the body of the annular U-cup piston seal.
The annular flange 13 is also angularly disposed sidewardly and radially of the piston seal and by still referring to FIG. 2 of the drawings, a vertical section of a piston 15 may be seen with a seal-receiving groove 16 annularly thereof. It will be observed that the smallest diameter of the piston seal 10 is smaller than the smallest diameter of the groove 16 in the piston 15. The piston 15 is mounted on a piston rod 18.
The piston seal 10 must be stretched and thereby distorted in placing it in the groove 16. When this occurs, the piston seal 10 assumes the configuration seen in FIG. 1 of the drawings. By referring to FIG. 1, it will be observed that the arcuate transverse plane of its smallest diameter has flattened out due to the distortion of installation as aforesaid. This results in the annular edge of the flange 12 which is rounded in a configuration resembling half of an O-ring sealingly engaging the adjacent surface of the piston.
When the piston with the seals mounted thereon, as seen in FIG. 1 of the drawings is installed in a cylinder, the flange 13 which is angularly disposed in its as-formed condition is distorted to a generally flat configuration so that it provides a sealing action with respect to the cylinder 17. Pressurized gas within the cylinder will also enter the annular groove 14 to further flatten flanges 12 and 13 against their respective surfaces. The area of the piston 15 between the annular grooves 16 provides for the positioning of a pair of annular bearing members 19.
As noted above, the piston seal 10 must be stretched and thereby distorted in placing it in the groove 16. There are instances however where it is not possible, or not desirable, to stretch and distort a seal. Conventionally, U-shaped cup seals have not been available in these instances. It would therefore be desirable if a cup seal were available where is not possible or desirable to stretch or distort a seal, such as when the seal is to be installed into a deep recess.
Further, when seal stretching and distortion occurs, seal material selection is limited. For example, in hot water seal applications, rubber is often used for seals because it has the necessary high elongation and flexibility properties, but rubber is difficult to use in friction fit applications, and the rubber seal exposed to hot water can fuse to a metal seat area.